The widget allows Pango markup to be used for input as an alternative to
set_text or for setting a default value when the widget is empty. The default
value when empty is ideal for standalone text entries that have no accompanying
label (such as a text field for a search).

This widget allows for the text data to be entered either through the normal
methods provided by Gtk2::Entry or to use the method /set_markup. It's
possible to switch between two methods for applying the text. The standard
Gtk2::Entry methods will always apply a text without styles while
set_markup() will use a style.